Protein catalysts, or enzymes, are useful in promoting reactions in various applications. For certain applications the enzyme must be immobilized on a suitable solid support. Immobilization may be accomplished by a variety of chemically-based approaches including adsorptive, ionic bonding, and covalent bonding techniques. Additionally, the catalyst may be entrapped in a gel or polymer matrix, stabilized in a micellar structure, incorporated into the substance of the matrix itself, or enclosed in a membrane using the so-called membrane-enclosed enzyme catalysis technique.
The immobilization procedures are, as a whole, difficult, expensive, and often only partially effective. For instance, one method requires soaking a polycarbonate membrane for 24 hours in a solution of poly-(L-lysine), rinsing, soaking the membrane in a buffered glutaraldehyde solution for 2 hours, washing, and finally soaking the membrane in a buffered glucose oxidase solution for 24 hours. This method relies on covalent bonding between the poly(L-lysine) layer and the polycarbonate membrane. This method is not effective unless the support medium and the poly(L-lysine) layer are capable of covalent bonding with each other. Another method immobilizes lipases by formation of enzyme-silicone polymer composites. This paper describes problems with binding to hydrophobic polymer surfaces, low catalyst densities in sol-gel entrapment methods, and limited application of crosslinked lipase preparations. To address these issues the paper describes adsorption of proteins onto poly(hydroxymethylsiloxane) [PHOMS], followed by reaction with silanol-terminated PDMS prepolymers, poly(diethylsilicate), and (3-aminopropylethoxysilane) crosslinker to form a solid silicone rubber with encapsulated lipase-PSOMS. Polysiloxanes are relatively expensive, however, and may not be a suitable support for many applications.
The goal in developing new methods of immobilizing enzymes is to enhance the ease, economy, and simplicity of achieving high enzymatic activity that persists for long periods of time at a defined location on a fixed surface or support. To achieve this goal it is desirable to have as high of a catalytic activity of an immobilized enzyme as possible and for the catalytic activity to be relatively stable. It would also be desirable to have a method of immobilizing an enzyme on a polymeric support that would be useful with many kinds of supports and enzymes.